Disorder-induced expansion of silicate minerals arises from the breakage of weak topological constraints

NMA Krishnan and Y Le Pape and G Sant and M Bauchy, JOURNAL OF NON- CRYSTALLINE SOLIDS, 564, 120846 (2021).

DOI: 10.1016/j.jnoncrysol.2021.120846

The disordering of the atomic network of minerals typically results in swelling of the structure. However, the origin of such expansion and the extent thereof remain unclear. Here, we conduct a series of molecular dynamics simulations of vitrification- and irradiation-induced disordering to reveal the nature of disorder-induced expansion in silicate phases. We show that pristine crystals are topologically overconstrained-i.e., some interatomic constraints are mutually redundant. Consequently, the weaker atomic constraints yield to the stronger ones- a behavior that manifests itself through some internal elastic stress in the network. Interestingly, we demonstrate that disordering results in a release of this internal stress by breaking the weaker constraints. The release of such internal strain explains the macroscopic expansion exhibited by atomic networks upon disordering.

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